Expanded-metal resistor and method of making the same



H. C. NAGEL. EXPANDED METAL RESISTOR AND METHOD OF MAKING THE SAME. APPLICATION FILED MAR-7.1919.

1,396,87 1 Patented Nov. 15,, 1921 Eye WITNESSES: INVENTOR ATTORNEY UNITED. STATES PATENT OFFICE.

HARRY C. NAGEL, OF WILKINSEURG, PENNSYLVANIA, ASSIGNOR TO WESTINGHOUSE ELECTRIC & MANUFACTURING COMPANY, A CORPORATION OF PENNSYLVANIA.

EXPANDED-METAL RESISTOR AND METHOD OF MAKING THE SAME.

an improved expanded-metal resistor and.

a novel method of making the same. In some cases, as where 1t 1s desired to control the circuits of electric motors on board ship, cast-grid resistors are unreliable because of their liability to become broken after repeated shocks, and wire resistors have not the required capacity. Liquid resistors, too, are obviously undesirable. Expanded-metal resistors have accordingly been tried. y

Ordinary expanded metal, however, is unsatisfactory for such uses because it cannot be obtained commercially with portions unexpanded or in the variety and degree of expansion to make it adaptable for resistor work. A common'method of manufacture, which comprises first, slitting the metal sheet and later, pulling the metal apart at the slits, is unsatisfactory because the width of the resulting product is less than that of the original sheet, the walls of some of the slits are pulled apart more than those of others, and, while some of the slit openings may .be larger than is necessary for resistor purposes, thus causing the resistor to occupy unnecessary additional space, others of the openings may be so small as to cause short-circuits.

According to the present invention, a strip of uncut metal is operated upon in such fashion as to simultaneously cut and stretch the metal, whereby the resulting product is of the same width as the original, uncut sheet. -The metal is stretchedin a direction oblique to the plane of the sheet so as to obtain comparatively large openings between the walls oftheslits without the necessity oftaking up a great deal of room in the plane of the grid. The openings are provided of just the proper size Specification of Letters Patent. Patented N 15, 1921, Application filed March 7, 1919. Serial No. 281,154. I

so that the maximum amount of resistor material is crowded into the minimum amount of space, without danger of short-circuits. The openings are further of symmetrical form to provide for the parallel resistance paths being of equal length. Uncut portions of the metal are left at the ends to serve as terminals. trical, series path, the expanded metal is longitudinally slotted. If a steel or similar alloy is employed, the metal is sherardized 'or otherwise protected against the weather.

Figure 1 of the accompanying drawing is a front view of an improved form of my expanded metal resistor and Fig. 2 is a side view thereof, looking in the direction of the arrows.

In forming my expanded-metal resistor, a sheet of metal. having the requisite electrical conductivity is first out along slits 1 to form a lengthened path for the electric current. The sheet is then moved longitudinally and to one side. The sheet is then cut at slits 2, opposite portions 9 that are not cut at'the previous operation. The sheet is then moved longitudinally in the same direction,

and to the other side, and is cut at slits 3- opposite the slits first made, and so on until as much of the sheethas been cut as is desired. Portions of the metal are left uncut at the ends, as shown at 4 and 5. Uncut portions may also, if desired, be left at the center and at other securing places.

Simultaneously with the slitting operation, the metal is stretched in a direct-ion oblique tothe plane of the sheet, by reason of the shape of the cutting tool, to produce openings 6 which shall be inclined to the plane of the sheet .whereby the walls of the openings shall be separated from each other to an appreciable extent, thereby avoiding short-circuits, but without occupying an unduly large amount of room in the plane of the sheet. Oblique stretching is obviously better for'this purpose than stretching either in the plane of the sheet or at right angles thereto. The simultaneous slitting and stretching is effected in such fashion that the portions of the openings 6 on each side of the metal portions 9 are of the same size and width." The parallel. paths of the current are thereby rendered equal in length.

By means of the simultaneous operations of slitting and stretching, there can be no contractionin the width of the metal, be-

To lengthen the eleccause the stretching operation is effected at a time when the metal that is being stretched iscontiguous to 'unstretched metal. The resulting product is therefore of the same Width as the unexpanded metal and is stiffer than ordinary expanded metal.

The metal is then slotted as at 7 to increase the electrical series path from one of the terminals 4, longitudinally through the grid to the terminal 5 and then back through the other portion of the grid to the other terminal 4, and openings 8 are punched,

one in the terminal portion 5 and one in each of the terminal portions 4 so as to provide for easily securing the resistor in position in a frame or box by means of bolts or similar. securing means. The metal may then-be 'sherardized or otherwise treated to defects of. ordinary expanded-metal resistors.

2. An expanded-metal resistor having an;

unexpanded portion and an expanded portion, the expanded portion belng formed by simultaneous cutting and stretching so as to be of the same Width as the unexpanded portion.

3. A slotted expanded-metal resistor having terminal unexpanded portions and an intermediate expanded portion, said resistor having a slot extending through one of said terminal, portions and said intermediate portion to said other terminal portion.

4. A resistor formed from a plane metal sheet having an expanded portion of the same Width as the said sheet.

5. A resistor formed from a rectangular metal sheet having an expanded portion and an unexpanded portion of equal Widths. 6. A resistor having expanded portions displaced from the plane of the resistor and extending obliquely thereto.

In testimony whereof, I have hereunto subscribed my name this 20th day of Feb, 1919.

HARRY C; NAGEL. 

